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Use the primary key in FileField and ImageField filenames

Author:
exogen
Posted:
October 12, 2008
Language:
Python
Version:
1.0
Score:
3 (after 5 ratings)

Sometimes it is desirable to use values like the primary key when naming FileField and ImageField files, but such values are only available after saving the model instance. This abstract class implements a two-phase save in order to make this case easy. See the example in the docstring.

Another solution would be to write a save() that requires upload_to to be a callable that checks for instance.pk, then calls it again after saving. However, this would require more work from the developer for simple cases. 

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from django.utils.encoding import force_unicode
import os.path

class RenameFilesModel(models.Model):
    """
    Abstract model implementing a two-phase save in order to rename
    `FileField` and `ImageField` filenames after saving.  This allows the
    final filenames to contain information like the primary key of the model.
    
    Example:
    
        class Photo(RenameFilesModel):
            file = models.ImageField(upload_to='uploads/temp')
            
            RENAME_FILES = {
                'file': {'dest': 'uploads/photos', 'keep_ext': True}
            }
        
        >>> photo = Photo(file='uploads/temp/photo.jpg')
        >>> photo.pk
        
        >>> photo.save()
        >>> photo.pk
        1
        >>> photo.file
        <ImageFieldFile: uploads/photos/1.jpg>
    
    If the 'dest' option is a callable, it will be called with the model
    instance (guaranteed to be saved) and the currently saved filename, and
    must return the new filename.  Otherwise, the filename is determined by
    'dest' and the model's primary key.
    
    If a file already exists at the resulting path, it is deleted.  This is
    desirable if the filename should always be the primary key, for instance.
    To avoid this behavior, write a 'dest' handler that results in a unique
    filename.
    
    If 'keep_ext' is True (the default), the extension of the previously saved
    filename will be appended to the primary key to construct the filename.
    The value of 'keep_ext' is not considered if 'dest' is a callable.
    
    """
    RENAME_FILES = {}
    
    class Meta:
        abstract = True
    
    def save(self, force_insert=False, force_update=False):
        rename_files = getattr(self, 'RENAME_FILES', None)
        if rename_files:
            super(RenameFilesModel, self).save(force_insert, force_update)
            force_insert, force_update = False, True
            
            for field_name, options in rename_files.iteritems():
                field = getattr(self, field_name)
                file_name = force_unicode(field)
                name, ext = os.path.splitext(file_name)
                keep_ext = options.get('keep_ext', True)
                final_dest = options['dest']
                if callable(final_dest):
                    final_name = final_dest(self, file_name)
                else:
                    final_name = os.path.join(final_dest, '%s' % (self.pk,))
                    if keep_ext:
                        final_name += ext
                if file_name != final_name:
                    field.storage.delete(final_name)
                    field.storage.save(final_name, field)
                    field.storage.delete(file_name)
                    setattr(self, field_name, final_name)
        
        super(RenameFilesModel, self).save(force_insert, force_update)

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Comments

grahamu (on December 16, 2008):

FWIW, this class did not work for me when running Django in Windows XP. Specifically, the field.storage.delete(file_name) call results in Windows "Error 32: The process cannot access the file because it is being used by another process".

#

abusquets (on March 21, 2009):

I have the same problem as grahamu

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nemesis (on November 16, 2010):

Nice one, thanks!

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giles (on May 16, 2013):

@grahamu @abusquets

To fix that error, you should close the file field before you delete it: field.close()

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philgyford (on February 26, 2018):

This almost works for me (using Django 2.0) but when it comes to field.storage.save(final_name, field) I get ValueError: seek of closed file. This is using local storage and the development webserver. I'm not sure how to get around this.

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